1. Field of the Invention
The present invention relates to an electrostatic discharge circuit, especially to a current-mirror-based electrostatic discharge clamping circuit and a current-mirror-based electrostatic discharge detector.
2. Description of Related Art
An electrostatic discharge (ESD) clamping circuit is capable of preventing an integrated circuit from the damage of electrostatic discharge. FIG. 1 illustrates a conventional ESD clamping circuit 100 including: a high-voltage terminal 110; a low-voltage terminal 120; a resistor 130; a capacitor 140; an inverter 150; and a switch 160. Under a normal mode (that is to say an ESD-free mode), the capacitor 140 blocks DC voltage while the voltage of the input end of the inverter 150 is a high voltage and the voltage of its output end is a low voltage, so that the switch 160 is not conductive due to the low voltage. Under an ESD mode, the capacitor 140 is not able to reflect the instant voltage variation of the high-voltage terminal 110 (because the voltage of a capacitor will not substantially change immediately) while the voltage of the input end of the inverter 150 is a low voltage and the voltage of its output end is a high voltage, so that the switch 160 is conductive due to the high voltage and carries out electrostatic discharge.
On the basis of the above, the capacitor 140 of the ESD clamping circuit 100 is usually a MOS (metal oxide semiconductor) capacitor in which the material of its gate layer could be electricity-conductive material (e.g. polysilicon) other than metal. However, in an advanced semiconductor process, the thickness of the gate layer is getting thinner and thinner, which leads to a more and more serious gate leakage problem. Consequently, the ESD clamping circuit 100 of FIG. 1 suffers the same problem, and gate leakage will pass through the capacitor 140 which is not supposed to be conductive ideally. This problem not only causes undesired power-consumption, but also makes the voltage of the input end of the inverter 150 unstable. The voltage of the input end may change from a high voltage to a low voltage under the aforementioned normal mode, which makes the switch 160 conductive improperly.
People who are interested in the prior art may refer to the following documents: U.S. Pat. Nos. 4,797,899, 5,946,177, 6,385,021, 6,724,603, 6,989,979 and 8,498,085.